(a) Field of the Invention
The present invention relates to a method and an apparatus for automatically measuring the thickness and roughness of wooden boards and, more particularly, but not exclusively, to a portable type apparatus for such use.
(b) Description of Prior Art
In the production of lumber, it is necessary to cut logs into usable boards which are then planed to remove irregularities therefrom resulting from the wear and tear of the saw blade. The sawdust produced in saw mills is considered an undesirable residue because of its low value as compared to wood chips which can be used in the production of building material. An analysis of saw mills has shown that the rough lumber produced has considerable thickness variation and data has revealed that the thickness of boards can vary, on the average, between 0.06 inch and 0.21 inch. The majority of the saws used are circular saws and the cutting edges of the saw are subjected to considerable wear due to the nature of the logs being cut and the heating of the blade. Thus, rough lumber is produced with substantial irregularities in the cut surface thereof. It is, therefore, necessary to plane such irregularities which result in an increased loss of lumber. As stated above, investigation has shown that the loss of lumber is approximately 0.15 inch in the width of the saw blade cut. This is considerable when taking into account that a log of 12 inch diameter is capable of producing approximately ten separate 1 inch boards in its cross-section. This means a loss of at least one board on such a log.
The above problem can be minimized by ensuring that the saw blade is always properly adjusted and that the cutting edge is in good condition whereby to maintain the saw cut substantially straight and of a minimum width and with minimum undulations or irregularities along its cut length.
The planing of such irregularities is also a time-consuming process which adds to the cost of the production. Also, the narrower the width of the saw cut, the less sawdust produced and the less loss of lumber. A great deal of attention is being given to the reduction of the saw blade thickness so that the width of the cut is further reduced whereby the production of sawdust is also reduced. However, the sawing accuracy, that is, maintaining the saw blade along an intended line of cut as closely as possible, is another factor which should be taken into consideration to minimize the irregularities or roughness in the lumber.
Various types of measuring apparatus have been developed in an attempt to measure the roughness, or thickness of the lumber, as it is cut in the sawmill. It is known to provide a gauge consisting of hand-held spring arms with an electric resistance strain gauge adapted thereto and to measure a piece of lumber at selected intervals of lengths therealong. In one attempt to solve this problem, a panel truck was fitted with equipment for sensing thickness by probes similar to the spring arms and resistance strain gauge arrangement mentioned above. Lumber was passed through slots in the side of the truck and five pairs of probes in the truck sensed thickness at five positions across the width of each board. The vehicle contained paper tape punches for recording data. However, such apparatus do not continuously sense the lumber thickness along a predetermined length thereof and preferably from end to end. Also, such apparatus could give false readings if a knothole or a wood chip hole is accidentally measured by one of the probes.